Method and apparatus for performing inter-carrier D2D communication

ABSTRACT

A system and method for use in a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE) is disclosed. The method for performing a discovery transmission on a second carrier by a user equipment (UE) served by a primary cell (PCell) on a first carrier, includes receiving, from a base station, a signaling indicating that the UE read discovery resource configuration for the second carrier on the second carrier or that the UE should request the discovery resource configuration for the second carrier from the base station for acquiring the discovery resource configuration for the second carrier. The method also includes acquiring the discovery resource configuration based on the signaling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/555,339,filed Aug. 29, 2019, now U.S. Pat. No. 11,228,893, which is a divisionalof application Ser. No. 15/230,326, filed Aug. 5, 2016, now U.S. Pat.No. 10,440,550, which claims priority to Indian Patent Application No.861/KOL/2015, filed Aug. 6, 2015, and Indian Patent Application No.1118/KOL/2015, filed Oct. 29, 2015, the entire disclosures of which areincorporated herein by reference.

BACKGROUND 1. Field

The present disclosure concerns methods and apparatuses for performinginter-carrier device-to-device (D2D) communication, and morespecifically, to methods and apparatuses for managing resources fortransmitting and receiving inter-carrier discovery signals.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G (4^(th)-Generation) communication systems, efforts havebeen made to develop an improved 5G (5^(th)-Generation) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘beyond 4G network’ or a ‘post LTE system’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 gigaHertz (GHz) bands, so as toaccomplish higher data rates. To decrease propagation loss of the radiowaves and increase the transmission distance, the beamforming, massivemultiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO),array antenna, an analog beam forming, large scale antenna techniquesare discussed in 5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud radioaccess networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, hybrid frequency shift key (FSK) and quadratureamplitude modulation (QAM) modulation (FQAM) and sliding windowsuperposition coding (SWSC) as an advanced coding modulation (ACM), andfilter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA),and sparse code multiple access (SCMA) as an advanced access technologyhave been developed.

Device to device (D2D) communication is being researched for enablingdiscovery and data communication services between user equipments (UEs).Discovery is a process for determining that a D2D-enabled UE is presentadjacent to another D2D-enabled UE. Discovering a D2D-enabled UEdetermines whether another D2D-enabled UE is interested in using D2Ddiscovery. A D2D-enabled UE may have interest in discovering anotherD2D-enabled UE when its proximity needs to be known by one or moreauthenticated applications by discovering a D2D-enabled UE. For example,a social networking application may be enabled to use D2D discovery. D2Ddiscovery may enable the D2D-enabled UE of a particular user of thesocial networking application to discover his friends' D2D-enabled UEsor allow for discovery by the friends' D2D-enabled UEs. As anotherexample, D2D discovery may enable discovery of, e.g., shops orrestaurants of interest, which are located near the D2D-enabled UE of aparticular of a search application. A D2D-enabled UE may discover othernearby D2D-enabled UEs using direct UE-to-UE signaling.

In a conventional method, when discovery is supported for a cell (orserving cell) camping on a carrier F1 to send discovery messages, a UEmay obtain discovery resources for sending discovery messages on the F1carrier from the serving cell on the F1 carrier. The serving cell maybroadcast discovery resource configurations in system information block19 (SIB 19). SIB 19 may deliver resource pools for transmission ofdiscovery messages. A UE may use such resources to send discoverymessages in an idle state. When there is no resource pool fortransmission or UE is in a connected state, a D2D UE should send arequest for resources for sending discovery messages on the F1 carrierto the serving cell on the F1 carrier using dedicated signaling.

In another conventional method, while camping on a serving cell on acarrier F1, a D2D UE may be permitted to send discovery messages onanother carrier F2. This may be referred to as inter-carrier discoverycommunication. Unless discovery is supported by the serving cell oncarrier F1 or carrier F1 is a frequency at which a D2D UE desires tosend discovery messages, the D2D UE may send discovery messages. Theserving cell on carrier F1 may provide an assistance for obtainingresources for discovery transmission on carrier F2. In other words, theserving cell may provide resources for discovery transmission on carrierF2 in SIB 19 or dedicated signaling.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

An issue with inter-carrier discovery transmission is how a UE issupposed to act when the UE is in the idle state, and a serving cell oncarrier F1 does not provide discovery resources for the other carrierF2. The UE enters a connected state and sends a request for resources oncarrier F2 to the serving cell on carrier F1. Otherwise, the UEmaintains the idle mode, read out SIB 19 on carrier F2, and autonomouslyobtain resources on carrier F2. In the former case, if the serving cellon carrier F1 offers no assistance, a transition to the connected statemay be useless, causing unnecessary signaling for allowing the idle UEto enter into the connected state. In the latter case, unnecessary powerconsumption may occur.

Another issue with inter-carrier discovery transmission concernssimultaneous transmission on F1 and F2 when the UE is in the connectedstate on carrier F1 and is conducting wireless wide area network (WAN)communication. When the UE fails to acquire an additional transmissionchain, the UE cannot simultaneously perform uplink (UL) transmission toa base station on carrier F1 and discovery transmission on carrier F2.Since uplink transmission is higher in priority, discovery transmissionmay be skipped by the UE. In order to enhance discovery performance, adiscovery TX gap can be generated. The discovery TX gap is a time slot(or subframe) on UL, where the UE need not perform transmission on UL.TX gaps can be added to existing gaps, such as discontinuous reception(DRX). During DRX, the UE need not perform reception on downlink (DL)nor transmission on UL. TX gaps need to be known to base station (oreNB) to prevent the base station from scheduling UL for the UE. Forinter-carrier discovery transmission, TX gaps, parameters for signalingTX gaps, and periodicity of TX gap signaling may come at issue. ULtransmission timing on carrier F1 and discovery transmission timing onF2 might not be aligned. Subframes for discovery transmission on carrierF2 and subframes for uplink transmission on carrier F1 may not bealigned because discovery transmission on carrier F2 is based on DLtiming whereas UL transmission on carrier F1 is based on timingadvanced. Further, DL transmission timings on carrier F1 and carrier F2might not be synced. Accordingly, UE or eNB determining TX gaps for ULsubframes corresponding to discovery subframes is a critical issue, anda method is required for UE or eNB to determine TX gaps on carrier F1corresponding to discovery subframes on carrier F2. Discovery messagesmay be periodically sent using dedicated resources or contention-basedresources. When using contention-based resources, the base station inthe serving cell on carrier F1 might not recognize resources (i.e.,discovery frames selected by the UE for discovery transmission from adiscovery resource pool configured on carrier F2).

To address the above-discussed deficiencies, it is a primary object toprovide a method and apparatus for addressing the above-described issuesin inter-carrier D2D communication.

Objects of the present disclosure are not limited to the foregoing, andother unmentioned objects would be apparent to one of ordinary skill inthe art from the following description.

To achieve the above objects, according to an embodiment of the presentdisclosure, a method for performing a discovery transmission on a secondcarrier by a user equipment (UE) served by a primary cell (PCell) on afirst carrier, comprises receiving, from a base station, a signalingindicating that the UE read discovery resource configuration for thesecond carrier on the second carrier or that the UE request thediscovery resource configuration for the second carrier from the basestation for identifying the discovery resource configuration for thesecond carrier, and identifying the discovery resource configurationbased on the signaling.

To achieve the above objects, according to an embodiment of the presentdisclosure, a method for performing a discovery transmission on a secondcarrier by a user equipment (UE) served by a primary cell (PCell) on afirst carrier, comprises determining at least one TX gap on the firstcarrier for the discovery transmission on the second carrier, andtransmitting, to a base station, a TX gap request including informationon at least one uplink subframe on the first carrier corresponding tothe at least one TX gap.

To achieve the above objects, according to an embodiment of the presentdisclosure, a user equipment (UE) served by a primary cell (PCell) on afirst carrier for performing a discovery transmission on a secondcarrier, comprises a transceiver, and a processor coupled to thetransceiver; wherein the processor is configured to receive, from a basestation, a signaling indicating that the UE read discovery resourceconfiguration for the second carrier on the second carrier or that theUE request the discovery resource configuration for the second carrierfrom the base station for identifying the discovery resourceconfiguration for the second carrier and identify the discovery resourceconfiguration based on the signaling.

To achieve the above objects, according to an embodiment of the presentdisclosure, a user equipment (UE) served by a primary cell (PCell) on afirst carrier for performing a discovery transmission on a secondcarrier, comprising a transceiver, and a processor coupled to thetransceiver; wherein the processor is configured to determine at leastone TX gap on the first carrier for the discovery transmission on thesecond carrier, and transmit, to a base station, a TX gap requestincluding information on at least one uplink subframe on the firstcarrier corresponding to the at least one TX gap.

Details of other embodiments are set forth in the detailed descriptionand the drawings.

Embodiments of the present disclosure present the following effects, atleast.

An efficient resource allocation method can be provided for supportinginter-carrier D2D communication.

Further, there is provided an apparatus capable of running an efficientresource allocation method is provided for supporting inter-carrier D2Dcommunication.

The effects of the present disclosure are not limited thereto, and thedisclosure encompasses other various effects.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the disclosure.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 is a view illustrating a wireless communication environmentaccording to an embodiment of the present disclosure;

FIG. 2 is a flowchart illustrating a process for configuring a TX gapaccording to an embodiment of the present disclosure;

FIG. 3 is a flowchart illustrating a process for configuring a TX gapaccording to an embodiment of the present disclosure;

FIG. 4 is a view illustrating the timing of DL and UL subframes on F1and F2;

FIG. 5 is a view illustrating a method for configuring a TX gapaccording to an embodiment of the present disclosure;

FIG. 6 is a view illustrating a method for configuring a TX gapaccording to an embodiment of the present disclosure;

FIG. 7 is a view illustrating a method for configuring a TX gapaccording to an embodiment of the present disclosure;

FIG. 8 is a view illustrating TX gap signaling parameters according toan embodiment of the present disclosure;

FIG. 9 is a view illustrating TX gap signaling parameters according toan embodiment of the present disclosure;

FIG. 10 is a view illustrating TX gap signaling parameters according toan embodiment of the present disclosure;

FIG. 11 is a flowchart illustrating a process for using reference signalreceived power (RSRP) of Pcell for selecting a discovery resource poolaccording to an embodiment of the present disclosure;

FIG. 12 is a view illustrating a measurement gap on F1 and a discoveryperiod on F2 according to an embodiment of the present disclosure;

FIG. 13 is a flowchart illustrating a process when RSRP of Pcell isavailable for selecting a discovery resource pool according to anembodiment of the present disclosure;

FIG. 14 is a flowchart illustrating a process when RSRP of Pcell isunavailable for selecting a discovery resource pool according to anembodiment of the present disclosure;

FIG. 15 is a flowchart illustrating a process for selecting a discoveryresource pool when information on discovery resource pools is deliverednot from Pcell but from another cell according to an embodiment of thepresent disclosure;

FIG. 16 is a flowchart illustrating a process for selecting a discoveryresource pool when information on discovery resource pools is deliverednot from Pcell but from another cell according to an embodiment of thepresent disclosure;

FIG. 17 is a flowchart illustrating a process for selecting a discoveryresource pool when information on discovery resource pools is deliverednot from Pcell but from another cell according to an embodiment of thepresent disclosure;

FIG. 18 is a flowchart illustrating a process for configuring a RX gapaccording to an embodiment of the present disclosure;

FIG. 19 is a view illustrating a configuration of a RX gap according toan embodiment of the present disclosure;

FIG. 20 is a view illustrating RX gap signaling parameters according toan embodiment of the present disclosure; and

FIG. 21 is a block diagram illustrating a base station or UE accordingto an embodiment of the present disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

FIGS. 1 through 21 , discussed below, and the various embodiments usedto describe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication system.

Advantages and features of the present disclosure, and methods forachieving the same may be understood through the embodiments to bedescribed below taken in conjunction with the accompanying drawings.However, the present disclosure is not limited to the embodimentsdisclosed herein, and various changes may be made thereto. Theembodiments disclosed herein are provided only to inform one of ordinaryskilled in the art of the category of the present disclosure. Thepresent disclosure is defined only by the appended claims.

Before getting into the detailed description of the present disclosure,particular terms or phrases used herein may be defined merely for easeof description. As used herein, the terms “include” and “comprise” andtheir derivatives may mean doing so without any limitations. As usedherein, the term “or” may mean “and/or.” As used herein, the phrase“associated with” and “associated therewith” and their derivatives maymean “include,” “be included within,” “interconnect with,” “contain,”“be contained within,” “connect to or with,” “couple to or with,” “becommunicable with,” “cooperate with,” “interleave,” “juxtapose,” “beproximate to, “be bound to or with, “have, or “have a property of” Asused herein, the term “controller” may mean any device, system, or partthereof controlling at least one operation. As used herein, the term“device” may be implemented in hardware, firmware, software, or somecombinations of at least two thereof. It should be noted that functions,whatever particular controller is associated therewith, may beconcentrated or distributed or implemented locally or remotely. Itshould be appreciated by one of ordinary skill in the art that thedefinitions of particular terms or phrases as used herein may be adoptedfor existing or future in many cases or even though not in most cases.

Although the terms “first” and “second” are used to describe variouscomponents, the components are not limited by the terms. These terms areprovided simply to distinguish one component from another. Accordingly,the first component mentioned herein may also be the second componentwithin the technical spirit of the present disclosure.

Although the terms “first” and “second” are used to describe variouscomponents, the components are not limited by the terms. These terms areprovided simply to distinguish one component from another. Accordingly,the first component mentioned herein may also be the second componentwithin the technical spirit of the present disclosure.

FIG. 1 is a view illustrating a wireless communication environmentaccording to an embodiment of the present disclosure. Referring to FIG.1 , a first base station 110 can provide a wide area network (WAN)wireless communication service to devices in its coverage through acarrier with a frequency f1. The first base station 110 can providewireless communication services using radio access technology (RAT),such as long term evolution (LTE), code division multiple access (CDMA),or global system for mobile communications (GSM), but not limitedthereto. The carrier with frequency f1 can be referred to as F1 carrieror carrier F1 or simply as F1. The term “base station” may be replacedwith other various terms denoting an entity providing wirelesscommunication service in particular coverage of a network or cell, suchas nodeB or evolved nodeB (eNB). In some embodiments, a base station canprovide one or more cells. Each cell can mean coverage provided at itscenter frequency. UE can be served from base station by multiple cellsprovided from one base station or two or more base stations. Multiplecells serving UE can be divided into a primary cell (PCell) and one ormore secondary cells (SCells).

A user equipment (UE) 120 can receive wireless communication servicefrom first base station 110 through a PCell on F1 carrier, and firstbase station 110 can be a serving base station for UE 120. UE 120 can beany one of a mobile phone, smartphone, personal digital assistant (PDA),laptop computer, net book, or internet of things (IoT) device, but notlimited thereto, or can be any device that can receive WAN wirelesscommunication service.

UE 120 can directly communicate with another UE 130 without using WAN.Such direct communication between devices can be denoteddevice-to-device (D2D) communication. UE 120 should detect that other UE130 is located adjacent to UE 120 in order to conduct D2D communication.For such detection, UE 120 can send discovery signal (or discoverymessage), and as other UE 130 located adjacent to UE 120 responds to thediscovery signal, D2D communication can begin. Discovery transmissiondescribed below may denote transmission of discovery signal (ordiscovery message). Discovery signal can be sent on an F2 carrier havinga frequency f2 different from f1. Transmission of discovery signal usinga carrier of a frequency different from a carrier used for communicationwith serving base station may be denoted inter-carrier discoverytransmission. In such case, first base station 110 providing wirelesscommunication service on F1 carrier may or may not support transmissionof discovery signal on F2 carrier. A need exists for methods for sendingdiscovery signals according to whether first base station 110 supportstransmission of discovery signal on F2 carrier.

A second base station 140 which is a non-serving base station for UE 120can provide wireless communication service through F2 carrier. Secondbase station 140 can support transmission of discovery signal on F2carrier. In such case, a need also exists for methods for sendingdiscovery signals using transmission of discovery signal on F2 carrierby second base station 140. In some embodiments, second base station 140can also be a serving base station for UE 120. In such case, second basestation can provide SCell to UE 120 through F2 carrier. In someembodiments, the first base station 110 can provide UE with a PCell onF1 carrier and a SCell on F2 carrier. In such case, the first basestation 110 and the second base station (140) can be a single entity.

Supporting by a base station discovery transmission of a UE can includesignaling a configuration of resources for transmission of discoverysignal (hereinafter, discovery resources) to the UE. Unless the servingbase station on F1 carrier signals discovery resource configuration forF2 carrier, the UE in a radio resource control (RRC) idle state canselect one of the following two options.

In the first option, the UE can attempt to read out system informationblock 19 (SIB 19) broadcast on F2 carrier. The UE can obtain thediscovery resource configuration for F2 carrier by reading out SIB 19and send discovery signal using the obtained resource configuration.System information block 19 (SIB 19) sent on F2 carrier can betransmitted from a base station (e.g., the base station 140 of FIG. 1 )other than the serving base station. In the first option, discoverytransmission and cell detection (i.e., detection of base station on F2carrier) on F2 carrier might not influence WAN operation. In someembodiments, the UE can attempt to read out SIB 19 sent on F2 carrierwhen the following conditions are met for the base station on F2carrier.

-   -   Srxlev>0 and Squal>0

Here,Srxlev=Q _(rxlevmeas)−(Q _(rxlevmin) +Q_(rxlevminoffset))−Pcompensation,Squal=Q _(qualmeas)−(Q _(qualmin) +Q _(qualminoffset)), and

Srxlev, cell selection RX level (decibel (dB))

Squal, cell selection quality (dB)

Q_(rxlevmeas), measured cell RX level (RSRP)

Q_(qualmeas), measured cell quality (reference signal received quality(RSRQ))

Q_(rxlevmin), minimum RX level required in cell (decibel milliwatts(dBm))

Q_(qualmin), minimum quality level required in cell (dB)

Q_(rxlevminoffset), offset for signaled Q_(rxlevmin) considering Srxlevassessment as a result of periodic discovery on higher-priority publicland mobile network (PLMN) while normally camping on visited PLMN(VPLMN)

Q_(qualminoffset), offset for signaled Q_(qualmin) considering Squalassessment as a result of periodic discovery on higher-priority PLMNwhile normally camping on VPLMN

Pcompensation, max(P_(EMAX)−P_(PowerClass), 0) (dB)

P_(EMAX), maximum TX power level (dBm) available to UE upon uplinktransmission in cell defined as P_(EMAX) in TS 36.101

P_(PowerClass), maximum RF output power (dBm) of UE as per UE powerclass as defined in TS 36.101.

In the second option, UE can send a discovery resource configuration forserving base station. UE should enter a RRC connected state to send arequest for discovery resource configuration to the serving basestation. UE can send a request for discovery resource configuration tothe serving base station through F1 carrier, and in response thereto,the serving base station can provide UE with a discovery resourceconfiguration on F2 carrier through dedicated signaling instead of SIB19. However, unless the serving network or serving base station providesdiscovery resource configuration through dedicated signaling, it may beuseless that UE enters the RRC connected state and requests discoveryresource configuration for discovery transmission on F2 carrier. Sincethe serving network or serving base station may recognize whether it canprovide an assistance (i.e., discovery resource configuration) forinter-carrier discovery transmission, it can be preferable to allow theserving network or serving base station to control UE to select one ofthe above-described two options for inter-carrier discoverytransmission.

In some embodiments, the base station provides an indication to UE forUE to select one of the two options in order for UE to obtain discoverresource configuration for F2 carrier. Specifically, the serving basestation sends an indication as to whether UE should read out SIB (e.g.,SIB 19) on F2 carrier or UE should send a request for discovery resourceconfiguration for F2 carrier to the serving cell. UE obtains a discoveryresource configuration for F2 carrier based on the received indication.The base station uses a one-bit indicator in the dedicated signaling orbroadcast signaling (i.e., SIB 19) to instruct UE to select one of thetwo options. The dedicated signaling or the broadcast signaling can betransmitted by the base station on F1 carrier.

In some embodiments, if the base station does not broadcast thediscovery resource configuration for F2 carrier on F1 carrier, the basestation indicates UE to select one of the two options.

In some embodiments, the base station, unless discovery resourceconfiguration for F2 carrier is included in SIB 19 on F1 carrier,provides an indication to UE as to whether UE should select the secondoption, using the one-bit indicator in the broadcast signaling (i.e.,SIB 19) or dedicated signaling. In some embodiments, unless there is theone-bit indicator, UE selects the first option. In some embodiments, theone-bit indicator indicates whether an assistance (i.e., discoveryresource configuration) for inter-carrier discovery transmission isprovided to the base station. In some embodiments, unless SIB 19 isbroadcast on F1 carrier by the serving base station, UE uses the secondoption.

In some embodiments, the (broadcast or dedicated) signaling transmittedby the base station for indicating UE to select one of the two optionscan also comprise indication for other carriers (e.g., F3 carrier, F4carrier) in addition to F2 carrier. For example, the signaling cancomprise an indication as to whether UE should read out SIB (e.g., SIB19) on F3 carrier or UE should send a request for discovery resourceconfiguration for F3 carrier to the serving cell, in order for UE toobtain discover resource configuration for F3 carrier.

An example of the signaling for the serving base station to instruct UEto select one of the two options is as follows.

SL-CarrierFreqInfo-v13x0::=  SEQUENCE {   discTxResources-r13 CHOICE    acquireSI-FromCarrier-r13   NULL,     discTxPoolCommon-r13  SL-DiscTxPoolListNFreq-r13,     requestDedicated-r13   NULL    noTxOnCarrier-r13   NULL   }    OPTIONAL, -- Need OR  discRxResources-r13 SL-DiscRxPoolListNFreq-r13    OPTIONAL  -- Need OR}

On each frequency, the base station can signal one of the following. TXresource pools (discTXPoolCommon-r13), indication(acquireSI-FromCarrier-r13) for reading out SIB 19 to obtain resourcesfrom the carrier of the frequency, indication (requestDedicated-r13) forsending a request for dedicated resources to serving cell, or indication(noTxOnCarrier) for banning transmission of discovery signal on carrierof the frequency. A list of the frequencies can be signaled separatelyfrom the above signaling, and the number of entries inSL-CarrierFreqInfo-v13x0 can be the same as the number of frequencies inthe frequency list. There can be one to one mapping between the entriesin SL-CarrierFreqInfo-v13x0 and the frequencies of the frequency list.The Nth entry in SL-CarrierFreqInfo-v13x0 corresponds to the Nthfrequency in frequency list.

Now described is a method for processing TX gap for discoverytransmission.

When UE does not have an additional TX chain for discovery transmission,UE cannot simultaneously conduct discovery transmission on F2 carrierand uplink transmission on F1 carrier. RRC-connected UE requests theserving base station to prevent uplink from being scheduled in subframeson F1 carrier overlapping subframes (i.e., discovery subframes) fordiscovery transmission on F2 carrier by sending a request for TX gap.Alternately, RRC-connected UE can request the serving base station toallow UE to prioritize discovery transmission over UL transmission insubframes on F1 carrier overlapping with subframes (i.e., discoverysubframes) for discovery transmission on F2 carrier by sending a requestfor TX gap. During TX gap, UE assigns a higher priority to discoverytransmission than to uplink transmission. When UE does not conductdiscovery transmission in TX gap, UE conducts uplink transmission. If UEis configured with multiple cells in the serving base station, UE cantransmit request for gap on PCell.

A method for configuring a TX gap is described below in greater detailwith reference to FIG. 2 . FIG. 2 is a flowchart illustrating a processfor configuring a TX gap according to an embodiment of the presentdisclosure.

Referring to FIG. 2 , UE 210 determines TX gaps necessary on F1 when UEdoes not have an additional TX chain for inter-carrier discoverytransmission (230). UE sends a request for discovery TX gap havinginformation on the determined TX gaps to serving eNB 220 (240). Theinformation on the determined TX gaps comprises frequency of F2 carrierand parameters indicating the determined TX gaps on F2 carrier. Thediscovery TX gap request can be sent through a SidelinkUEInformationmessage. UE 210 puts priority to discovery transmission on F2 ratherthan UL transmission on F1 during TX gaps (250). In some embodiments, ifsubframe for discovery transmission on F2 overlaps with UL TX on F1during the TX gap and UL TX on F1 is not related to random accessprocedure (e.g., RACH preamble transmission or MSG3 transmission) thenUE prioritize to transmit discovery over UL transmission. If subframefor discovery transmission on F2 overlaps with UL TX on F1 during the TXgap and UL TX on F1 is related to random access procedure (e.g., RACHpreamble transmission or MSG3 transmission) then UE prioritize ULtransmission over discovery transmission in that subframe. Serving eNB220, upon receiving the discovery TX gap request, provides TX gaps in 0or more UL subframes on F1 that can overlap subframe for discoverytransmission on F2 (260).

In some embodiments, serving eNB does not provide a gap for all of thesubframes indicated by UE in the TX gap request. In some embodiments,serving eNB abstains from providing a response (i.e., TX gap response)to the TX gap request. When subframe for discovery transmission on F2overlaps UL TX on F1 during TX gap, UE conducts discovery transmissionbefore UL transmission. Alternatively, when subframe for discoverytransmission F2 overlaps UL TX on F1 except for sounding referencesignal (SRS) and physical uplink control channel (PUCCH) during TX gap,UE sends discovery signal. RRC-connected UE monitors downlink (physicaldownlink control channel (PDCCH) or enhanced PDCCH (EPDCCH)) andmonitors whether UL is scheduled or not in subframes on F1 (on physicaluplink shared channel (PUSCH)) corresponding to discover subframes fordiscovery transmission on F2. Data on PUSCH can be dynamicallyscheduled, and scheduling information can be indicated in PDCCH orEPDCCH. UE can also be scheduled to send control information on PUCCHfor feedback of scheduling request (SR) or hybrid automatic repeatrequest (HARD). When type 1 resource is allocated in order to avoidcollision between transmission of PUCCH, SRS, or physical random accesschannel (PRACH) of UE on F1 carrier and discovery transmission on F2carrier, UE excludes discovery subframes on F2 carrier overlappingPUCCH, SRS, or PRACH transmission on F1 carrier before selectingresources for discovery transmission from the discovery resource pool.Here, type 1 resource allocation means a discovery resource allocationscheme in which a particular discovery resource pool for UE amongmultiple discovery resource pools is allocated to UE by base station,and UE selects resource (i.e., subframe) for discovery transmission fromthe allocated discovery resource pool. Meanwhile, type 2 resourceallocation means a discovery resource allocation scheme in whichdedicated discovery resource is allocated to UE by base station.

Another method for configuring a TX gap is described below withreference to FIG. 3 . FIG. 3 is a flowchart illustrating a process forconfiguring a TX gap according to an embodiment of the presentdisclosure.

In FIG. 3 , operations 330, 340, 350, and 370, respectively, aresubstantially the same in description as operations 230, 240, 260, and370 of FIG. 2 . In operation 360, serving eNB 320 sends a TX gapresponse including information on TX gaps allocated by the serving eNB320 to UE 310. The information on TX gaps includes frequency of F2carrier and parameters indicating TX gaps allocated on F2 carrier. TheTX gap response can be delivered through a RRCConnection Reconfigurationmessage.

In an embodiment, the TX gap response indicates whether UE's request(i.e., discovery TX gap request) is accepted. The presence of TX gaps inthe TX gap response indicates that UE's request is accepted. Whenaccepted (i.e., TX gaps are provided in the TX gap response), UE neednot perform UL transmission in TX gaps which are UL subframes signaledby UE in the TX gap request, and discovery transmission has priorityover UL transmission during TX gaps.

In another embodiment, the TX gap response indicates whether UE'srequest is accepted. When accepted, eNB gives an indication of TX gaps(i.e., UL subframes where UE need not do UL transmission) to UE, ordiscovery transmission can have priority over UL transmission. The TXgap response can be sent on F1 carrier by serving eNB albeit no requestis made (unsolicited) (i.e., without TX gap request). For example, whenserving eNB on F1 carrier allocates dedicated resources for discoverytransmission on F2 carrier, the TX gap response can be sent despiteunsolicited.

In another embodiment, the TX gap response can give UE an indicationthat UE need not perform UL transmission in the TX gaps (i.e., ULsubframes corresponding to discovery subframes for discoverytransmission on F2 carrier). UE may be already aware of discoverysubframes used for discovery transmission.

In another embodiment, the TX gap response can give UE an indicationthat UE need not perform UL transmission in the TX gaps (i.e., ULsubframes corresponding to discovery subframes for discoverytransmission on F2 carrier), i.e., that discovery transmission haspriority over UL transmission.

In some embodiments, UE sends a TX gap request only when type 1 resourceallocation scheme is used for discovery transmission. When type 2resource allocation scheme is used, serving eNB on F1 carrier, becauseof being aware of discovery resources used by UE for discoverytransmission on F2 carrier, determines TX gaps even when no TX gaprequest is made.

In some embodiments, UE also sends a TX gap request regardless ofresource allocation schemes (whether it is of type 1 or type 2).

In some embodiments, UE sends a TX gap request for all of the discoverysubframes in the discovery resource pool allocated to UE. In someembodiments, UE sends a request for TX gaps for subframes allocated toUE for discovery transmission or discovery subframes selected by UE. Insome embodiments, eNB provides TX gaps corresponding to one or moresubframes, and UE selects one of them for discovery transmission.

A method for determining TX gap by UE is now described.

UE sends information on TX gaps (i.e., one or more subframes whereserving eNB should abstain from scheduling UL or UE should not beexpected to conduct any UL transmission) to serving eNB. UE recognizesdiscovery subframes on F2 carrier carrying discovery messages, and UEcan thus determine TX gaps corresponding to discovery subframes.

While discovery transmission on F2 carrier is based on DL timing, uplinktransmission on F1 carrier is based on timing advanced, and thus,discovery transmission on F2 carrier and uplink transmission on F1carrier might not be aligned. Further, DL transmission timing on F1carrier and DL transmission timing on F2 carrier might not be synced.This is described in more detail with reference to FIG. 4 .

FIG. 4 is a view illustrating the timing of DL and UL subframes on F1and F2. In FIG. 4 , eNB1 is a serving base station for UE and uses F1carrier, and eNB2 is a base station on F2 carrier. The DL subframe in UEon F1 carrier can come behind, by t1, DL subframe timing in eNB1 on F1carrier. The value t1 is a propagation delay between UE and eNB1. ULsubframe timing on F1 carrier in UE can come ahead, by t2, of DLsubframe timing in eNB on F1 carrier. The value t2 is a timing advance.DL subframe timing in eNB2 on F2 carrier might not be identical to DLsubframe timing on F1 carrier due to a sync failure. The DL/D2D subframetiming in UE on F2 carrier can come behind, by t3, DL subframe timing ineNB2 on F2 carrier. The value t3 is a propagation delay between UE andeNB2. Resultantly, a gap of t4 exists between UL subframe timing in UEon F1 carrier and DL/D2D subframe timing on F2 carrier.

Regarding the start time of UL subframe on F1 carrier, UE determines atime gap (i.e., t4) for D2D subframe on F2 carrier. The method forconfiguring TX gap can be varied by t4, which is described below in moredetail with reference to FIGS. 5 to 7 .

FIG. 5 is a view illustrating a method for configuring a TX gap,particularly when t4 is 0, according to an embodiment of the presentdisclosure. Since t4 is 0, when discovery signal is transmitted in ULsubframe i+1 520 in UE on F2 carrier, TX gap is required only in ULsubframe i+1 510 on F1 carrier. That is, when t4 is 0, only one ULsubframe can be required on F1 carrier where TX gap is configured foreach discovery subframe on F2 carrier.

FIG. 6 illustrates a method for configuring TX gap according to anotherembodiment, particularly when t4 is the same as gap 630 at the end ofthe subframe for D2D transmission on F2 carrier. Gap can be configuredbetween subframes for DL or D2D transmission on F2 carrier as well. Whent4 is the same as gap 630 at the end of subframe for D2D transmission onF2 carrier, substantially no signal is sent from UE during gap 630, andthus, when discovery signal is sent in UL subframe i+1 620 in UE on F2carrier, TX gap is required only in UL subframe i+1 610 on F1 carrier.That is, when t4 is the same as gap 630 at the end of subframe for D2Dtransmission on F2 carrier, only one UL subframe can be required on F1carrier where TX gap is configured for each discovery subframe on F2carrier, and this is also true for where t4 is less than gap 630 at theend of subframe for D2D transmission on F2 carrier.

FIG. 7 illustrates a method for configuring TX gap according to anotherembodiment, particularly when t4 is larger than gap 740 at the end ofthe subframe for D2D transmission on F2 carrier. When t4 is larger thangap 740 at the end of subframe for D2D transmission on F2 carrier, TXgaps can be configured in UL subframe i+1 710 and subframe i+2 720 on F1carrier temporally overlapping region except for gap 740 in subframe i+1730 on F2 carrier in order to insure discovery transmission in D2Dsubframe i+1 730 on F2 carrier.

In some embodiments, regardless of what is shown in FIGS. 5 to 7 , UEdetermines necessary TX gap in UL subframe on F1 carrier which starts orends during discovery subframe on F2 carrier. In some embodiments,regardless of what is shown in FIGS. 5 to 7 , UE determines necessary TXgap in UL subframe on F1 carrier which starts or ends during discoverysubframe on F2 carrier or at the boundary of discovery subframe. Suchembodiments can be useful for when UE is on the move, and after UEdetermines TX gaps, t4 varies.

In some embodiments, TX gap in UL subframe on F1 carrier determined bythe above-described schemes can be required only when UL subframedetermined as TX gap is not configured as D2D subframe in F1 carrier.

In some embodiments, determination of TX gaps can be made by UEregardless of whether dedicated resources (i.e., type 2 resourceallocation or scheduled resource allocation) or contention-basedresources (i.e., type 1 resource allocation or UE selection resourceallocation) are used for discovery transmission on F2 carrier. In someembodiments, determination of TX gaps can be performed by UE whencontention-based resources (i.e., type 1 resource allocation or UEselection resource allocation) are used for discovery transmission on F2carrier.

In some embodiments, additional subframes or times other than subframewhere UE sends discovery signal can be considered in determining TXgaps. For example, subframes on F2 carrier for transmission of device todevice sync signal and interruption time for retuning from F1 carrier toF2 carrier or from F2 carrier to F1 carrier, as well as one or moresubframes for transmission of discovery signal (i.e., one or moresubframes on F2 carrier where discovery resources for discoverytransmission are configured) should be taken into account fordetermining TX gap. Subframe offset between subframes on carrier F1 andcarrier F2 should also be taken into account when determining the TXgaps. The same can be individually signaled in TX gap request.Alternatively, the same can be indicated as TX gap.

A method for determining TX gap by eNB is described below.

UE sends information on discovery subframes on F2 carrier to servingeNB, or otherwise, serving eNB may already recognize discovery subframesused by UE for discovery transmission. In such case, serving eNB needsto determine TX gaps on F1 carrier. In some embodiments, serving eNB hassignaled discovery subframes used by UE for discovery transmission andcan thus be aware of them.

In some embodiments, UE determines a difference (i.e., t4) in start timebetween D2D subframe on F2 carrier and UL subframe on F1 carrier. UEsends information on t4 to eNB at a TX gap request. eNB determines avalue obtained by subtracting t1 from the start time of DL subframe onF1 carrier in eNB as the start time of UL subframe on F1 carrier in UE.The value of time t1 has been known to eNB. The eNB determines a valueobtained by subtracting t4 from the start time of UL subframe on F1carrier in UE as the start time of D2D subframe on F2 carrier in UE.Thereafter, eNB determines TX gaps using the same method as thatperformed by UE before.

In some embodiments, a value obtained by subtracting t1 from the starttime of DL subframe on F1 carrier in eNB can be determined as the starttime of UL subframe on F1 carrier in UE. The value of time t1 has beenknown to eNB. Thereafter, eNB determines a difference in start timebetween UL subframe on F1 carrier in UE and DL subframe on F2 carrier.The start of DL subframe on F2 carrier in UE can be regarded as start ofdiscovery subframe on F2 carrier. Since eNB can be aware of offsetbetween DL transmission timings on F1 carrier and F2 carrier, the starttime of DL subframe on F2 carrier can have been known to eNB. The eNBdetermines that TX gap is needed in UL subframe on F1 carrier thatstarts or ends during discovery subframe on F2 carrier or at theboundary of discovery subframe on F2 carrier.

In some embodiments, eNB regards the start of D2D transmission timing onF2 carrier as DL timing on F1 carrier, and eNB determines that TX gap isneeded in UL subframe on F1 carrier that starts or ends during discoverysubframe on F2 carrier or at the boundary of discovery subframe on F2carrier.

In some embodiments, TX gaps can be computed by UE or eNB for discoverysubframes actually sent by UE. In other embodiments, TX gaps can becomputed for each discovery subframe in discovery resource pool.

Periodicity of TX gap request is described below.

The periodicity of TX gap request can be varied depending on methods forconfiguring discovery resources.

There can be a number of TX resource pools, and a TX resource pool canbe selected based on RSRP. In such case, UE may have to reselectresource pool when RSRP is varied. As a result, resources for discoverytransmission may be varied in each discovery period. Whether a newresource pool needs to be selected or not can be based on RSRPmeasurement before discovery period. Accordingly, UE might not send a TXgap request on multiple discovery periods. UE may have to send a TX gaprequest in each discovery period.

There may be a number of TX resource pools, and a TX resource pool canbe randomly selected. In such case, UE selects resource pool andresources for multiple discovery periods. Accordingly, UE sends one TXgap request every “N” discovery periods.

There may be a single TX resource pool. In such case, UE may have torandomly select resources for each transmission in each discoveryperiod. As a result, resources selected for discovery transmission maybe varied in each discovery period. UE can randomly select resources formultiple discovery periods and send one TX gap request every “N”discovery periods.

TX gap signaling parameters are now described.

TX gap signaling parameters can be used to indicate TX gaps in TX gaprequest. UE sends one discovery message in each discovery period. Eachdiscovery protocol data unit (PDU) can be sent multiple times indiscovery period, and accordingly, TX gap for multiple subframes may beneeded. Since discovery subframes may be varied in discovery period, TXgaps may also be varied. Accordingly, TX gaps can be signaled usingsubframe bitmap.

According to an embodiment of the present disclosure, the followingparameters can be used to signal TX gaps at TX gap request.

TX gap period, periodicity of TX gaps

offset, difference between start of first TX gap period and SFN=0

TX gap list, includes one or more elements in list, and each elementincludes SubframeBitMap or SubframeBitMapOffset.

SubframeBitMap, variably sized bitmap. The nth SubframeBitMap in the TXgap list corresponds to the nth gap interval subsequent to gap intervalwhere TX gap request is sent. Each bit indicates whether subframe is TXgap or not.

SubframeBitMapOffset, offset between start of TX gap period and firstsubframe indicated by SubframeBitMap. SubframeBitMapOffset might not bepresent in the first element in list. In some embodiments,SubframeBitMapOffset may be present in none of the elements.

This is described in more detail with reference to FIG. 8 . FIG. 8 is aview illustrating TX gap signaling parameters according to an embodimentof the present disclosure. Referring to FIG. 8 , TX gap period candenote the length of TX gap period corresponding to discovery period andcan be indicated in unit of subframe. SubframeBitMap can indicatewhether at least some of subframes in a corresponding TX gap period areTX gap or not. When TX gaps 810 corresponding to discovery TX subframes820 are configured in first three subframes in the gap period as shownin FIG. 8 , SubframeBitMap can be configured in three bits, andSubframeBitMapOffset might not be present. In a gap period subsequent tothe gap period shown in FIG. 8 , SubframeBitMapOffset can denote periodsfrom the start timing of the corresponding gap period to subframeindicated by SubframeBitMap and can be indicated in unit of subframe.

According to an embodiment of the present disclosure, the followingparameters can be used to signal TX gaps at TX gap request.

TX gap list, includes one or more elements in list, and each elementincludes SubframeBitMapStart or SubframeBitMap.

SubframeBitMapStart, subframe # of subframe corresponding to mostsignificant bit of SubframeBitMap. In some embodiments, system framenumber (SFN) can be indicated instead of subframe #.

SubframeBitMap, variably sized bitmap. The most significant bit (MSB) ofSubframeBitMap corresponds to subframe indicated by SubframeBitMapStart.Each bit indicates whether subframe is TX gap or not.

This is described in more detail with reference to FIG. 9 . FIG. 9 is aview illustrating TX gap signaling parameters according to an embodimentof the present disclosure. Referring to FIG. 9 , SubframeBitMapStart maydenote the first subframe (i.e., subframe corresponding to MSB ofSubframeBitMap) of subframes indicated by SubframeBitMap indicating TXgaps 910 corresponding to discovery TX subframes 920.

According to another embodiment of the present disclosure, the followingparameters can be used to signal TX gaps at TX gap request.

One or more lists of SubframeBitMap and SubframeBitMapOffset

SubframeBitMap, variably sized bitmap. Each bit indicates whethersubframe is TX gap or not.

SubframeBitMapOffset, offset from SFN=0 of the first subframe indicatedby SubframeBitMap.

According to another embodiment of the present disclosure, the followingparameters can be used to signal TX gaps at TX gap request.

One or more lists of SFN and SubframebitMap

SubframebitMap (10 bits), each bit corresponds to subframe in SFN. MSBcorresponds to subframe of SFN.

According to another embodiment of the present disclosure, the followingparameters can be used to signal TX gaps at TX gap request.

TX gap period, periodicity of TX gaps

offset, difference between start of first TX gap period and SFN=0

TX gap list, includes one or more elements in list, and each elementincludes SubframeBitMapList.

SubframeBitMapList, variably sized bitmap list. The nthSubframeBitMapList corresponds to the nth gap interval subsequent to gapinterval where TX gap request is sent. Each element inSubframeBitMapList includes SubframeBitMap and SubframeBitMapOffset.

SubframeBitMap, variably sized bitmap. The nth SubframeBitMap in listcorresponds to the nth gap interval subsequent to gap interval where TXgap request is sent. Each bit indicates whether subframe is TX gap ornot.

SubframeBitMapOffset, offset between start of TX gap period and firstsubframe indicated by SubframeBitMap. SubframeBitMapOffset might not bepresent in the first element in list. In some embodiments,SubframeBitMapOffset may be present in none of the elements.

According to another embodiment of the present disclosure, the followingparameters can be used to signal TX gaps at TX gap request.

TX gap list, includes one or more lists of SubframeBitMapStart andSubframeBitMapList.

SubframeBitMapStart, subframe # of subframe corresponding to mostsignificant bit of SubframeBitMap. In some embodiments, system framenumber (SFN) can be indicated instead of subframe #.

SubframeBitMapList, variably sized bitmap list. Each element inSubframeBitMapList includes SubframeBitMap and SubframeBitMapOffset.

SubframeBitMap, variably sized bitmap. The first subframe bitmap beginsin the subframe number indicated in SubframeBitMapStart. For the rest,subframe bitmap starts at the offset (SubframeBitMapOffset) from thelast subframe indicated by a previous subframe bitmap. Each bitindicates whether subframe is TX gap or not.

SubFrameBitMapOffset, indicates offset of start of SubFrameBitMap forprevious bitmap in list. Offset can be indicated as the number ofsubframes or frames. In some embodiments, SubFrameBitMapOffset might notbe present for the first element in SubFrameBitMapList. In someembodiments, SubFrameBitMapOffset can be present in the first element inSubFrameBitMapList, and offset of start of subframe bitmap can beindicated from the subframe/frame number indicated bySubFrameBitMapStart.

This is described in more detail with reference to FIG. 10 . FIG. 10 isa view illustrating TX gap signaling parameters according to anembodiment of the present disclosure. Referring to FIG. 10 ,SubFrameBitMapStart indicates the first subframe among subframes wherewhether TX gap or not is indicated by the firstSubFrameBitMap(SubframeBitMap1). SubFrameBitMapOffset denotes aninterval between SubFrameBitMap1 and SubFrameBitMap(SubFrameBitMap2)subsequent to SubFrameBitMap1.

In some embodiments, UE signals a one-bit indicator indicating whetheradjacent subframes corresponding to TX gap signaled in TX gap requestshould also be TX gap.

UE reports TX gaps using the above-described signaling parameters oneach frequency where UE independently send discovery signal or UEindicates TX gap on all frequencies. For example, UE can send discoverysignal on F1 carrier and F2 carrier. UE can have serving cell on F3carrier and F4 carrier. Accordingly, UE can independently report TX gapson F1 carrier and F2 carrier. Alternatively, UE combines gaps necessaryfor F1 carrier and F2 carrier and report the combined gaps in TX gaprequest. While sending TX gap request, UE indicates serving cell orfrequency (or carrier) requiring TX gap. UE can also indicate frequencyon which UE want to transmit discovery signal. For example, whendiscovery transmission on F1 carrier requires gap on serving frequencyF3, UE can indicate gap necessary on frequency F3. In other embodiments,UE might not report frequency, and gap can be applied to all servingcells or serving frequencies.

The above-described signaling parameters can also be available to eNBfor configuring TX gaps.

RSRP measurement for inter-carrier discovery transmission is describedbelow.

Type 1 discovery resource allocation including multiple resource poolsand in which resource pool selection is based on RSRP may be availablefor discovery transmission. In such case, UE needs to measure RSRP forF2 carrier where discovery signal is sent for selecting resource pool.Resources for F2 carrier can be configured by serving cell on F1carrier. Alternatively, resources for F2 carrier can be obtained by UEreading out SIB (i.e., SIB 19) on F2 carrier.

For discovery resource allocation, Pcell (or serving cell or servingeNB) can indicate DL carrier available for selecting pool usingparameter UseRSRPPcell, carrier index, or absolute radio-frequencychannel number (ARFCN). Such indication can be achieved for each carriersupportive of discovery transmission. Alternatively, a list of carrierswhere Pcell's RSRP is available can be indicated in SIB 19. Unless RSRPof Pcell is available for discovery on F2 carrier, Pcell can configuremeasurement gap. This is described in more detail with reference to FIG.11 .

FIG. 11 is a flowchart illustrating a process for using RSRP of Pcellfor selecting a discovery resource pool according to an embodiment ofthe present disclosure. Referring to FIG. 11 , UE 1110 sends discoveryTX resource request to serving eNB 1120 (1130). The discovery TXresource request can be sent through a SidelinkUEinformation message.Serving eNB 1120 provides Pcell or serving cell for UE. When receivingdiscovery TX resource request, serving eNB 1120 determines whether UE1110 can use RSRP of Pcell to select resource pool for discoverytransmission (1140). Unless RSRP of Pcell can be used for selectingresource pool, serving eNB 1120 can configure measurement gap for UE1110 to perform measurement on F2 carrier (1150). Serving eNB 1120 sendsdiscovery resource pools for F2 carrier, parameter UserRSRPPcell, ormeasurement gap to UE 1110. Such information can be sent through aRRCConnection Reconfiguration message. When it is indicated that RSRP ofPcell is available by Pcell (i.e., serving eNB 1120) (e.g., throughparameter UseRSRPPcell), UE 1110 uses RSRP of Pcell for selectingresource pool. Otherwise (i.e., when RSRP of Pcell is indicated asunavailable), measurement on F2 carrier can be carried out (1170).Measurement on F2 carrier can be performed in the measurement gapnotified of by serving eNB 1120.

Measurement gap is described below in further detail with reference toFIG. 12 . FIG. 12 is a view illustrating a measurement gap on F1 and adiscovery period on F2 according to an embodiment of the presentdisclosure. Measurement gap repletion period (MGRP) which means theperiod of measurement gap 1210 can be set to be the same as discoveryperiod. Measurement gap 1210 can be sorted so that measurement gapduration is positioned before discovery period starts. In someembodiments, measurement gap duration can be set to 6 ms.

In some embodiments, Pcell on F1 carrier can indicate whether UE can useRSRP of Pcell to select resource pool on F2 carrier in broadcastsignaling (e.g., SIB). Unless RSRP of Pcell is available, UE sends arequest for measurement gap using a portion of TX gap request or a newmessage. This is described in more detail with reference to FIGS. 13 and14 .

FIG. 13 is a flowchart illustrating a process when RSRP of Pcell isavailable for selecting a discovery resource pool according to anembodiment of the present disclosure. Serving eNB 1320 broadcasts F2carrier type 1 discovery resource pools and UseRSRPPcell using SIB 19(1330). SIB 19 can be broadcast on F1 carrier. UseRSRPPcell parametercan be set to 1, indicating that RSRP of Pcell is available forselecting resource pool on F2 carrier. When receiving SIB 19 includingUseRSRPPcell and type 1 discovery resource pools of F2 carrier, UE 1310can use RSRP of Pcell to select discovery resource pool on F2 carrier(1340).

FIG. 14 is a flowchart illustrating a process when RSRP of Pcell isunavailable for selecting a discovery resource pool according to anembodiment of the present disclosure. Serving eNB 1420 broadcasts F2carrier type 1 discovery resource pools and UseRSRPPcell using SIB 19(1430). SIB 19 can be broadcast on F1 carrier. UseRSRPPcell parametercan be set to 0, indicating that RSRP of Pcell is unavailable forselecting resource pool on F2 carrier. When recognizing that RSRP ofPcell is unavailable for selecting resource pool on F2 carrier fromUseRSRPPcell parameter, UE 1410 determines to send a request formeasurement gap to Pcell (1440). UE 1410 sends TX gap request andmeasurement gap request on F1 carrier to serving eNB 1420 (1450).Measurement gap request or TX gap request can contain information ondiscovery period. Serving eNB 1420 sends information on measurement gapon F1 carrier to UE 1410. Measurement gap can be delivered through anRRCConnection Reconfiguration message. Measurement gap determined byserving eNB and sent to UE 1410 can be substantially the same as themeasurement gap described above in connection with FIG. 12 . Whenreceiving information on measurement gap, UE 1410 performs measurementon F2 carrier during measurement gap (1470). UE 1410 selects discoveryresource pool in subsequent discovery period based on measurement on F2carrier during measurement gap.

In some embodiments, resources on F2 carrier might not be configured byPcell. UE sends a request for measurement gap, indicate carrierinformation, and indicate discovery period and discovery offset forSFN=0. An offset can be selected so that there is a sufficient timebetween the start of discovery period on F2 carrier and measurementduration or termination of measurement gap. The eNB indicates whether UEuses RSRP of Pcell to select discovery resource pool using dedicatedsignaling. Unless RSRP of Pcell is available for selecting discoveryresource pool on F2 carrier, Pcell can configure measurement gap. Insome embodiments, MGRP can be set to be the same as discovery period.Measurement gap 1210 can be sorted so that measurement gap duration ispositioned before discovery period starts. Measurement gap duration canbe set to 6 ms. This is described in more detail with reference to FIG.15 .

FIG. 15 is a flowchart illustrating a process for selecting a discoveryresource pool when information on discovery resource pools is deliverednot from Pcell but from another cell according to an embodiment of thepresent disclosure. The eNB2 1530 sends information on type 1 discoveryresource pools for F2 carrier (1540). Information on type 1 discoveryresource pools can be broadcast on F2 carrier using SIB 19. The eNB21530 can be a base station operating on F2 carrier which does not serveUE 1510 on F1 carrier. When receiving the information on type 1discovery resource pools, UE 1510 sends discovery period and carrierinformation to serving eNB 1520. The carrier information can beinformation regarding carrier (i.e., F2 carrier) for UE 1510 to senddiscovery signal. The discovery period and carrier information can beincluded and sent in TX gap request or measurement gap request. ServingeNB 1520 determines whether UE can use RSRP of Pcell to select discoverresource pool (1560). Serving eNB 1520 sends UseRSRPPcell, a parameterwhose value is set based on the determination in operation 1560, to UE1510 (1570). When it is determined in operation 1560 that RSRP of Pcellcannot be used for selecting discovery resource pool, serving eNB 1520sends information regarding measurement gap, along with the UseRSRPPcellparameter, to UE 1510. The parameter UseRSRPPcell and measurement gapcan be sent through a RRCConnection Reconfiguration message. When RSRPof Pcell is indicated as available for selecting discovery resource poolby Pcell (i.e., serving eNB 1520), UE 1510 uses RSRP of Pcell forselecting discovery resource pool. Otherwise, UE 1510 conductsmeasurement for selecting discovery resource pool using the receivedinformation regarding measurement gap (1590).

In some embodiments, lists of other carriers where RSRP is available forselecting discovery resource pool can be broadcast by cell on F2carrier. This is described below in further detail with reference toFIG. 16 .

FIG. 16 is a flowchart illustrating a process for selecting a discoveryresource pool when information on discovery resource pools is deliverednot from Pcell but from another cell according to an embodiment of thepresent disclosure.

The eNB2 1630 broadcasts type 1 discovery resource pools on F2 carrierand parameter UseRSRPOtherCell using SIB (e.g., SIB 19) (1640).Parameter UseRSRPOtherCell can contain a list of other carriers (exceptfor F2 carrier) where RSRP is available for selecting discovery resourcepool. When RSRP of Pcell (i.e., serving eNB 1620) is indicated asavailable by cell (i.e., eNB2 1630) on F2 carrier, UE 1610 uses RSRP ofPcell to determine discovery resource pool, and can otherwise determineto request measurement gap (1650). When it is determined in operation1650 to send a request for measurement gap, UE 1610 sends a measurementgap request or TX gap request including carrier information anddiscovery period to serving eNB 1620 (1660). Serving eNB 1620 determineswhether UE 1610 can use RSRP of Pcell to select discover resource pool(1670). Serving eNB 1620 sends RRCConnectionReconfigurationMessageincluding measurement gap and parameter UseRSRPPcell indicating whetherUE 1610 can use RSRP of Pcell for selecting discovery resource pool toUE 1610 (1680). When RSRP of Pcell is indicated as available forselecting discovery resource pool by Pcell (i.e., serving eNB 1620), UE1610 uses RSRP of Pcell for selecting discovery resource pool.Otherwise, UE 1610 can conduct measurement for selecting discoveryresource pool using the received information regarding measurement gap(1690). Serving eNB 1620, when RSRP of Pcell is unavailable, canconfigure a measurement gap according to the information on measurementgap sent to UE 1610 in operation 1680 (1695).

In some embodiments, lists of other carriers where RSRP is available forselecting discovery resource pool can be broadcast by cell on F1carrier. This is described in more detail with reference to FIG. 17 .

FIG. 17 is a flowchart illustrating a process for selecting a discoveryresource pool when information on discovery resource pools is deliverednot from Pcell but from another cell according to an embodiment of thepresent disclosure. Referring to FIG. 17 , serving eNB 1720 canbroadcast parameter UseRSRPOtherCell using SIB (e.g., SIB 19) (1740).Parameter UseRSRPOtherCell can contain a list of other carriers (exceptfor F2 carrier) where RSRP is available for selecting discovery resourcepool. The eNB2 1730 can broadcast type 1 discovery resource pools on F2carrier using SIB (e.g., SIB 19) on F2 carrier (1745). When RSRP ofPcell (i.e., serving eNB 1720) is indicated as available for selectingdiscovery resource pool on F2 carrier, UE 1710 can use RSRP of Pcell forselecting discovery resource pool on F2 carrier, and can otherwisedetermine to request measurement gap (1750). When it is determined inoperation 1750 to send a request for measurement gap, UE 1710 can send ameasurement gap request or TX gap request including carrier informationand discovery period to serving eNB 1720 (1755). Serving eNB 1720 candetermine whether UE 1710 can use RSRP of Pcell to select discoverresource pool (1770). Serving eNB 1720 can sendRRCConnectionReconfigurationMessage including measurement gap andparameter UseRSRPPcell indicating whether UE 1710 can use RSRP of Pcellfor selecting discovery resource pool to UE 1710 (1770). When RSRP ofPcell is indicated as available for selecting discovery resource pool byPcell (i.e., serving eNB 1720), UE 1610 can use RSRP of Pcell forselecting discovery resource pool. Otherwise, UE 1710 can conductmeasurement for selecting discovery resource pool using the receivedinformation regarding measurement gap (1780). Serving eNB 1720, whenRSRP of Pcell is unavailable, can configure a measurement gap accordingto the information on measurement gap sent to UE 1710 in operation 1770(1790).

Hereinafter, RX gap for receiving inter-carrier discovery signal isdescribed.

When UE does not have an additional RX chain, UE cannot simultaneouslyreceive downlink on serving carrier (i.e., F1 carrier) and discoverysignal on another carrier (i.e., F2 carrier). In order to performdiscovery reception on F2 carrier, RRC-connected UE can request servingeNB to abstain from scheduling downlink (i.e., providing RX gap) insubframes on F1 carrier overlapping discovery subframes on F2 carrier bysending RX gap request. The RX gap request can be signaled using asidelinkUEInformation message. This is described in more detail withreference to FIG. 18 .

FIG. 18 is a flowchart illustrating a process for configuring a RX gapaccording to an embodiment of the present disclosure. Referring to FIG.18 , UE 1810 can identify that UE 1810 does not have an additional RXchain for inter-carrier discovery reception (1830). When UE 1810 doesnot have additional RX chain for inter-carrier discovery reception, UE1810 sends a SidelinkUEInformation message containing discovery RX gaprequest having RX gap information to serving eNB 1820. Serving eNB 1820determines to provide RX gap in one or more subframes indicated by UEusing RX gap information (1850). Serving eNB 1820 sendsRRCConnectionReconfiguration message containing discovery RX gapresponse having RX gap information to UE 1810. UE 1810 abstains frommonitoring DL in subframes indicated in RX gap information contained indiscovery RX gap response and can receive inter-carrier discovery insuch subframes (1870).

Subframes for discovery reception on F2 carrier and subframes fordownlink reception on F1 carrier might not be aligned due to a syncfailure between transmission times on F1 carrier and F2 carrier. This isdescribed in more detail with reference to FIG. 19 . FIG. 19 is a viewillustrating a configuration of a RX gap according to an embodiment ofthe present disclosure. As shown in FIG. 19 , up to two RX gaps 1910 ofsubframes may be needed for each discovery subframe 1920 on F2 carrier.Information on RX gaps 1910 (i.e., one or more downlink subframes whichshould not be scheduled for downlink by serving eNB) can be sent in RXgap request. Alternatively, UE can indicate subframes for discoveryreception on F2 carrier in RX gap request. Serving eNB can determinedownlink subframes overlapping subframes for discovery reception on F2carrier. In such case, eNB should be able to recognize timing gapbetween D2D subframe on F2 carrier and downlink subframe on F1 carrier.

When receiving RX gap request, serving eNB may or may not provide RX gapfor all subframes indicated by UE in RX gap request. RX gap response cangive UE an indication as to subframes (i.e., subframes not required tobe monitored by UE) where serving eNB is determined to provide RX gap.

RX gap response indicates whether UE's request is accepted or not. Whenaccepted, UE need not perform any DL reception in DL subframe signaledby UE in RX gap request. Alternatively, RX gap response indicateswhether UE's request is accepted or not. When accepted, eNB gives UE anadditional indication as to DL subframes where UE need not conduct anyDL reception.

FIG. 20 is a view illustrating RX gap signaling parameters according toan embodiment of the present disclosure. Referring to FIG. 20 , RX gapscan be indicated in RX gap request or RX gap response using thefollowing parameters.

RXGapPeriod, indicates periodicity of RX gaps. Duration is the same asdiscovery period.

RXGapOffset, indicates the start position for SFN=0 of RX gap period.

RXGapSubfameBitMap, bitmap indicating subframes requiring RX gap.

RXGapSubframeBitMapRepetition, indicates the number of times ofrepetition of RXGapSubfameBitMap.

In some embodiments, RXGapSubframeBitMapRepetition might not besignaled, and RXGapSubfameBitMap may have a variable size N, instead. Insome embodiments, multiple RXGapSubframeBitMap's is signaled.

According to the present disclosure, base station or UE is now describedwith reference to FIG. 21 . FIG. 21 is a block diagram illustrating abase station or UE according to an embodiment of the present disclosure.

The UE is first described. The UE 2100 can be configured to perform theUE's operations described above. Referring to FIG. 9 , the UE 2100includes a processor 2110, a memory 2120, and a transceiver 2130. Theprocessor 2110 is communicably and electrically connected with thememory 2120 and the transceiver 2130. The UE 2100 can transmit orreceive signals and communicate with other entities through thetransceiver 2130. The memory 2120 stores information for operations ofthe UE 2100. The memory 2120 can store commands or codes for controllingthe processor 2110. The processor 2110 can be configured to control theoperation of the UE 2100. The above-described operations of the UE 2100can be processed and run substantially by the processor 2110. Althoughtransmission or reception of signals is performed through thetransceiver 2130, and storage of data and commands is carried out by thememory 2120, the operations of the transceiver 930 and the memory 2120can be controlled by the processor 910, and thus, transmission andreception of signals and storage of data and commands can also be deemedto be performed by the processor 2110.

The base station is now described. The base station 2100 can beconfigured to perform the operation of base station, Pcell, serving eNB,or eNB2 as described above. The base station 2100 includes a processor2110, a memory 2120, and a transceiver 2130. Substantially the samedescription given above for UE can apply to the processor 2110, memory2120, and transceiver 2130.

It may be further appreciated by one of ordinary skill in the art thatvarious exemplary logic blocks, modules, circuits, methods, andalgorithms described in connection with embodiments described herein maybe implemented in hardware, computer software, or a combination thereof.In order to clarify interchangeability between hardware and software,various exemplary components, blocks, modules, circuits, methods, andalgorithms have been generally described in light of theirfunctionality. Whether such functionality is implemented in hardware orsoftware relies on a particular application and design limitations givento the overall system. The disclosed functionality may be embodied invarious manners on each particular application by one of ordinary skillin the art, but such determination should not be interpreted as causingdeparture from the category of the present disclosure.

Various exemplary logic blocks, modules, and circuits described hereinin embodiments the present disclosure may be implemented or performed bya general-purpose processor, digital signal processor (DSP), applicationspecific integrated circuit (ASIC), field programmable gate array (FPGA)or other programmable logic device, discrete gate or transistor logic,discrete hardware components, or their combinations designed to carryout the functions disclosed herein. The general-purpose processor may bea microprocessor. Alternatively, the processor may be a commonprocessor, controller, microcontroller, or state machine. Further, theprocessor may be implemented in a combination of computing devices,e.g., a combination of a DSP and a microprocessor, multiplemicroprocessors, one or more microprocessors integrated with a DSP core,or any other configurations.

The methods and algorithms described in connection with embodimentsdescribed herein may be directly implemented in hardware, a softwaremodule run by the processor, or in a combination thereof. The softwaremodule may reside in a random access memory (RAM), flash memory, readonly memory (ROM), erasable programmable ROM (EPROM), electricallyerasable programmable ROM (EEPROM), registers, hard disk, removabledisk, compact disc ROM (CD-ROM) or any other type of storage mediumknown in the art. The storage medium may be combined with the processorso that the processor reads information out of the storage medium andrecord information in the storage medium. Alternatively, the storagemedium may be integrated with the processor. The processor and storagemedium may reside in an ASIC.

In one or more exemplary embodiments, the above-described functions maybe implemented in hardware, software, firmware, or any combinationthereof. When implemented in software, the functions may be stored asone or more instructions or codes in a computer readable medium ortransmitted through the same. The computer readable medium includes botha communication medium and computer storage medium including any mediumfacilitating to transfer a computer program from one place to another.The storage medium may be any available medium accessible by ageneral-purpose or special-purpose computer. As a non-limiting example,such computer readable medium may include a RAM, ROM, EEPROM, CD-ROM orother optical disc storage, magnetic disk storage or other magneticstorage devices, or any other medium available for transferring orstoring program code means in a desired form of instructions or datastructures and accessible by a general-purpose or special-purposecomputer or special-purpose processor. Further, the access means isproperly denoted the computer readable medium. For example, when thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, optical fiber cable, twisted pair, digitalsubscriber line (DSL), or infrared (IR) rays, or wireless techniquesusing wireless and microwaves, the coaxial cable, optical fiber cable,twisted pair, DSL, IR rays, and wireless techniques using wireless andmicrowaves belong to the definition of the medium. As used herein, theterm “disk” or “disc” encompasses compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk, and Blu-ray disc, andhere, the disk reproduces data generally magnetically while the discreproduces data optically using laser beams. Combinations of thosedescribed above should be included in the computer readable medium.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method, performed by a base station on a firstcarrier, for providing discovery resource pool information to one ormore user equipments (UEs), the method comprising: identifyinginformation among first information, second information, thirdinformation and fourth information, for a second carrier among aplurality of carriers; and transmitting system information includingcarrier frequency information of the second carrier, wherein the carrierfrequency information of the second carrier includes the identifiedinformation for the second carrier, wherein the first informationincludes discovery resource pool information of the second carrier,wherein the second information indicates to obtain the discoveryresource pool information of the second carrier by reading a systeminformation block (SIB) transmitted on the second carrier, wherein thethird information indicates to obtain the discovery resource poolinformation of the second carrier by requesting the base station on thefirst carrier, and wherein the fourth information indicates not totransmit a discovery message on the second carrier.
 2. The method ofclaim 1, wherein the system information further includes carrierfrequency information of the plurality of carriers, and wherein each ofthe carrier frequency information of the plurality of carriers includesinformation among first information, second information, thirdinformation and fourth information, for each of the plurality ofcarriers.
 3. The method of claim 1, further comprising: receiving, froma UE among the one or more UEs, a request for the discovery resourcepool information of the second carrier in case that the carrierfrequency information of the second carrier includes the thirdinformation for the second carrier.
 4. The method of claim 1, wherein incase that the carrier frequency information of the second carrierincludes the second information for the second carrier, the SIBtransmitted on the second carrier is read at a UE to obtain thediscovery resource pool information of the second carrier.
 5. A basestation for providing discovery resource pool information to one or moreuser equipments (UEs) on a first carrier, the base station comprising: atransceiver; and at least one processor coupled to the transceiver andconfigured to: identify information among first information, secondinformation, third information and fourth information, for a secondcarrier among a plurality of carriers; and transmit system informationincluding carrier frequency information of the second carrier, whereinthe carrier frequency information of the second carrier includes theidentified information for the second carrier, wherein the firstinformation includes discovery resource pool information of the secondcarrier, wherein the second information indicates to obtain thediscovery resource pool information of the second carrier by reading asystem information block (SIB) transmitted on the second carrier,wherein the third information indicates to obtain the discovery resourcepool information of the second carrier by requesting the base station onthe first carrier, and wherein the fourth information indicates not totransmit a discovery message on the second carrier.
 6. The base stationof claim 5, wherein the system information further includes carrierfrequency information of the plurality of carriers, and wherein each ofthe carrier frequency information of the plurality of carriers includesinformation among first information, second information, thirdinformation and fourth information, for each of the plurality ofcarriers.
 7. The base station of claim 5, wherein the at least oneprocessor is further configured to receive, from a UE among the one ormore UEs, a request for the discovery resource pool information of thesecond carrier in case that the carrier frequency information of thesecond carrier includes the third information for the second carrier. 8.The base station of claim 5, wherein in case that the carrier frequencyinformation of the second carrier includes the second information forthe second carrier, the SIB transmitted on the second carrier is read ata UE to obtain the discovery resource pool information of the secondcarrier.
 9. A method, performed by a user equipment (UE) in a radioresource control (RRC) idle state served by a base station on a firstcarrier, for obtaining discovery resource pool information, the methodcomprising: receiving, from the base station, system informationincluding carrier frequency information of a second carrier, wherein thecarrier frequency information of the second carrier includes informationamong first information, second information, third information andfourth information for the second carrier among a plurality of carriers;and identifying the information for the second carrier, wherein thefirst information includes discovery resource pool information of thesecond carrier, wherein the second information indicates to obtain thediscovery resource pool information of the second carrier by reading asystem information block (SIB) transmitted on the second carrier,wherein the third information indicates to obtain the discovery resourcepool information of the second carrier by requesting the base station onthe first carrier, and wherein the fourth information indicates not totransmit a discovery message on the second carrier.
 10. The method ofclaim 9, wherein the system information further includes carrierfrequency information of the plurality of carriers, and wherein each ofthe carrier frequency information of the plurality of carriers includesinformation among first information, second information, thirdinformation and fourth information, for each of the plurality ofcarriers.
 11. The method of claim 9, further comprising: transmitting,to the base station, a request for the discovery resource poolinformation of the second carrier in case that the carrier frequencyinformation of the second carrier includes the third information for thesecond carrier.
 12. The method of claim 9, further comprising: readingthe SIB transmitted on the second carrier to obtain the discoveryresource pool information of the second carrier, in case that thecarrier frequency information of the second carrier includes the secondinformation for the second carrier.
 13. A user equipment (UE) in a radioresource control (RRC) idle state, served by a base station on a firstcarrier for obtaining discovery resource pool information, the UEcomprising: a transceiver; and at least one processor coupled to thetransceiver and configured to: receive, from the base station, systeminformation including carrier frequency information of a second carrier,wherein the carrier frequency information of the second carrier includesinformation among first information, second information, thirdinformation and fourth information for the second carrier among aplurality of carriers; and identify the information for the secondcarrier, wherein the first information includes discovery resource poolinformation of the second carrier, wherein the second informationindicates to obtain the discovery resource pool information of thesecond carrier by reading a system information block (SIB) transmittedon the second carrier, wherein the third information indicates to obtainthe discovery resource pool information of the second carrier byrequesting the base station on the first carrier, and wherein the fourthinformation indicates not to transmit a discovery message on the secondcarrier.
 14. The UE of claim 13, wherein the system information furtherincludes carrier frequency information of the plurality of carriers, andwherein each of the carrier frequency information of the plurality ofcarriers includes information among first information, secondinformation, third information and fourth information, for each of theplurality of carriers.
 15. The UE of claim 13, wherein the at least oneprocessor is further configured to transmit, to the base station, arequest for the discovery resource pool information of the secondcarrier in case that the carrier frequency information of the secondcarrier includes the third information for the second carrier.
 16. TheUE of claim 13, wherein the at least one processor is further configuredto read the SIB transmitted on the second carrier to obtain thediscovery resource pool information of the second carrier, in case thatthe carrier frequency information of the second carrier includes thesecond information for the second carrier.